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Addressing the life cycle of sewers in contrasting cities through an eco-

efficiency approach

Anna Petit-Boix, Carla Arnal, Desirée Marín, Alejandro Josa, Xavier Gabarrell, Joan

Rieradevall

Address correspondence to: Anna Petit-Boix (anna.petit@uab.cat) – Sostenipra, Institute

of Environmental Science and Technology, Universitat Autònoma de Barcelona (UAB),

Edifici ICTA-ICP, Carrer de les Columnes, 08193 Bellaterra, Barcelona, Spain.

KEYWORDS: water cycle, life cycle assessment, life cycle costing, industrial ecology,

eco-innovation

SUMMARY

Evaluating the sustainability of the urban water cycle is not straightforward,

although a variety of methods have been proposed. Given the lack of integrated data

about sewers, we applied the eco-efficiency approach to two case studies located in

Spain with contrasting climate, population, and urban and sewer configurations. Our

goal was to determine critical variables and life cycle stages and provide results for

decision-making. We used life cycle assessment (LCA) and life cycle costing (LCC) to

evaluate their environmental and economic impacts. Results showed that both cities

have a similar profile albeit their contrasting features, i.e., operation and maintenance

(O&M) was the main environmental issue (50-70% of the impacts) and pipe installation

registered the greatest economic capital expenditure (70-75%) due to labor. The location

of the wastewater treatment plant (WWTPs) is an essential factor in our analysis mainly

due to the topography effects, e.g., annual pump energy was thirteen times greater in

Calafell. Using the eco-efficiency portfolio, we observed that sewers might be less eco-

efficient than WWTPs and that we need to envision their design in the context of an

integrated WWTP-sewer management to improve sewer performance. In terms of

methodological approach, the bi-dimensional nature of eco-efficiency enables the

benchmarking of product systems and might be more easily interpreted by the general

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public. However, there are still some constraints that should be addressed to improve

communication, such as the selection of indicators discussed in the paper.

<Heading Level 1> Introduction

Meeting sustainability standards in cities is essential to ensuring the provision of

urban services at low environmental, economic and social costs. One of these services is

the urban water system, which calls for special attention given the increasing demand

for water and sanitation that results from growing urban populations (UN 2012).

However, evaluating the sustainability of this system is not straightforward. A variety of

methods can be applied to assess the performance of the urban water cycle. For

instance, multiple indicators have been used to cover some environmental, economic,

socio-cultural, and/or functional criteria (Balkema et al. 2002; Venkatesh and Brattebø

2013; Hellström et al. 2000; van Leeuwen et al. 2012; Muga and Mihelcic 2008; Lemos

et al. 2013; Fragkou et al. 2016). These were often combined through multi-criteria

approaches to assess diverse sustainability objectives at different scales (Makropoulos

et al. 2008; Marques et al. 2015).

Still, objective and comparable quantification is a challenge. We need to provide

robust models and data to water facility managers so that they can apply the most viable

options. In this respect, the eco-efficiency concept, normalized through ISO

14045:2012, can be particularly useful. This standard describes eco-efficiency

assessment as “a quantitative management tool which enables the study of life-cycle

environmental impacts of a product system along with its product system value for a

stakeholder”. This tool lacks the social dimension of sustainability (Ehrenfeld 2005),

but eco-efficiency is especially attractive because it might provide intrinsic information

about potential social benefits (Ekins 2005). For instance, the product system value

might be defined through consumer preferences. The need for a consistent approach

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(Brattebø 2005) is covered through ISO 14045:2012, which sets a methodological

framework for assessing the eco-efficiency of products and systems.

In the field of urban water management, the eco-efficiency of sewer networks is

worth analyzing. In general, there is an apparent interest in the absolute and relative

environmental impacts of wastewater treatment plants (WWTP) around the world

(Corominas et al. 2013), which have mainly been evaluated through life cycle

assessment (LCA). However, few of these LCAs include the pipe infrastructure (Loubet

et al. 2014). As opposed to WWTPs, which are generally affected by climatic

conditions, a particularity of sewers is the effect of urban configuration on the energy

required to operate the system (Petit-Boix et al. 2015). Within the existing literature,

articles have mainly focused on the environmental impacts of the construction or full

life cycle of sewers (Morera et al. 2016; Vahidi et al. 2015, 2016, Petit-Boix et al. 2016,

2014; Venkatesh et al. 2009; Risch et al. 2015) and a few studies have provided

economic data (Akhtar et al. 2014; Thomas et al. 2016; Murla et al. 2016). Only

Lorenzo-Toja et al. (2016) conducted an eco-efficiency benchmarking of WWTPs

following ISO 14045:2012, but sewers were not analyzed.

In this context, what are the hotspots that might alter the eco-efficiency of

sewers? Our goal was to apply the eco-efficiency approach to sewer networks in order

to determine critical variables and life cycle stages and provide results and discussion

for decision-making in the context of the urban water cycle. To address our questions,

we based our assessment on two cities with contrasting urban conditions and climate in

an attempt to represent major areas of the globe, i.e., an Atlantic city with year-round

population and a Mediterranean, coastal city with seasonal population. To quantify the

eco-efficiency of the systems, we followed the guidelines described in ISO 14045:2012.

<Heading level 1> Materials and Methods

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<Heading level 2> Case study definition

To answer our research question, we studied two Spanish cities with different

urban and climatic features in the framework of the LIFE+ Aquaenvec project

(LIFE10/ENV/ES/520). These cities present different conditions that we used to test

whether the eco-efficiency of sewers varies depending on the climate, population, and

sewer and urban configurations. Betanzos is located in the northwest of Spain and has

an Atlantic climate that results in more than 1,000 mm of rainfall every year.

Wastewater flows from households to a WWTP located at sea level and most of the

network is a gravity sewer due to the topography. In contrast, Calafell is a coastal,

Mediterranean city with an annual rainfall of around 500 mm. Because of land price and

usually odor control, the WWTP was constructed inland and 40 m above sea level,

which results in greater pumping requirements and length of sewer than in Betanzos

(table 1). Both cities can be considered medium-sized based on their population (10,000

– 50,000 inhabitants), although in Calafell it usually doubles in the summer (Idescat

2016).

The sewer components were identified through the water managers and the SGO

(Operation Management System) and CONTEC (Technical Control of the Integral

Water Cycle) databases (©Suez services company 2012). These were mainly combined

sewers, with a portion of stormwater network in Calafell. The network has a total length

of 77 and 173 km in Betanzos and Calafell, respectively. They consisted of concrete,

fibrocement, high-density polyethylene (HDPE) and polyvinylchloride (PVC) pipes.

Both cities had a greater share of plastic pipes, i.e., 66% of PVC in Betanzos and 73%

of HDPE in Calafell, and diameters of 300-315 mm dominated (50-75% of the

network). In the case of sewer appurtenances, the number of manholes and inspection

chambers was estimated assuming one unit every 50 meters of sewer (Petit-Boix et al.

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2014). The CONTEC database provided the number of scuppers, wastewater

connections and submersible pumps (©Suez services company 2012). However, the

power of the pumps was unknown and we tested a scenario with a 60 m3/h pump to

account for pump production, which is the highest flow we found in construction

databases (MetaBase ITeC 2010). We did know the real electricity consumption of the

system, and the wastewater production was registered at the WWTP.

<Table 1>

<Heading level 2> Eco-efficiency assessment method

The methodological framework of an eco-efficiency assessment combines the

environmental and value assessment of a product system (ISO 14045:2012). To do so,

ISO 14045:2012 includes two specific requirements for choosing eco-efficiency

indicators. The ratio between the environmental and value dimensions can either depict

an improved environment at the same product system value or an improved product

system value at the same environmental effect. These results can be represented through

eco-efficiency portfolios that illustrate the pathway towards the desired eco-efficiency

and can be used in the benchmarking of a product system using optimization functions.

For a given functional unit (FU), practitioners should define the indicators applied, as

these are not provided by the standard and might vary depending on the analysis.

In general, this ISO standard is relatively open and flexible in terms of

methodological approaches. LCA is the method selected to conduct the environmental

analysis based on ISO 14040:2006. In the case of the value assessment, the standard

calls for an integration of the full life cycle of the product system, but does not establish

a specific method for this type of analysis. Based on this ISO, the system value (i.e., its

worth or desirability) can be functional, monetary or intangible (i.e., esthetic, cultural,

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etc.). Because of the life cycle perspective, we typically apply life cycle costing (LCC;

ISO 15686-5:2008) and assess the monetary value of a product system. We used this

method in our analysis to assess the costs associated with the sewer infrastructure.

<Heading level 2> Goal and scope definition

In this study, we aim to assess the eco-efficiency of sewers by combining the

environmental and economic dimensions through the LCA and LCC methods. The FU

was the transport of one m3 of urban wastewater from the households to the WWTP in a

medium-sized city through a sewer network. We considered different lifespans

depending on the pipe material and sewer component. We assumed 100 years for

concrete pipes (U.S. Army Corps of Engineers 1998; CPSA 2010) and 50 years for

plastic pipes (UNE 53331:1997). A lifespan of 50 years was assigned to all types of

appurtenances except for submersible pumps, which were replaced every 10 years

(Petit-Boix et al. 2014).

To determine the environmental and economic results per FU, we followed the

method proposed by Petit-Boix et al. (2014). Based on EN 15804:2011, we set different

declared units for the construction assets, i.e., one linear meter of pipe-trench

constructive solutions and one unit of each appurtenance. To account for the total

impacts of the system, we scaled to the total sewer components (table 1) and combined

with the operation and maintenance (O&M) of the system.

The same system boundaries were considered in the LCA and LCC (figure 1).

These included the raw material procurement, pipe production, transport to the

construction site, pipe installation and trench preparation, and O&M. The demolition

was excluded because it was negligible (Petit-Boix et al. 2014; Gabarrell et al. 2013).

The end-of-life stage was not accounted for because the pipe can be either disposed of

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or left underground. The LCA does not include the emissions that result from

wastewater degradation on its way to the WWTP, such as methane, nitrous oxide, and

hydrogen sulfide, because a model is still needed to predict the emissions of the entire

network. According to Eijo-Río et al. (2015), these emissions might represent at least

4% of the O&M impacts and should be accounted for in future assessments.

<Figure 1>

<Heading level 2> Life cycle inventory (LCI)

Table 2 provides a detailed inventory of the material and energy flows involved

in the life cycle of the sewers in Calafell and Betanzos. Note that the production and

installation stage includes the pipes and appurtenances. The LCI of each sewer

component is provided in Appendix S1. When inventorying the pipelines, we

considered different trench designs depending on the pipe material. Based on the results

reported by Petit-Boix et al. (2016), we adapted the worst designs to show the

maximum environmental impacts of the system. Concrete pipe trenches had a bedding

factor of 4, which is the highest safety level (EN 1916:2002) and consists of the largest

amount of concrete bedding. Plastic pipes were embedded in sand imported from other

areas. The excavated soil was left aside for other purposes and its management was

outside of our scope. The appurtenance design was adapted from the literature (Petit-

Boix et al. 2014) and databases (MetaBase ITeC 2010; CYPE Ingenieros 2015).

Data on the energy consumed in the installation process and the materials used

in the pipe production were retrieved from MetaBase ITeC (2010). A truck covered a

distance of 100 km to transport plastics and metals to the construction site and 30 km to

transport the remaining materials (Doka 2003). The ecoinvent v2.2 database

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(Frischknecht et al. 2005) was used to obtain background information on the life cycle

of the materials and processes involved.

The O&M consisted of different variables. First, the energy required to pump

wastewater to the WWTP was provided by the facility managers. The electricity was

modeled using the Spanish mix of the year 2011 (REE 2012), which is the year that we

obtained data from. Second, the length of sewer and number of appurtenances renovated

every year was unknown. We assumed a certain number of repositions depending on

their lifespan, e.g., when a component had a 50-year lifespan, we considered one

reposition in 100 years. Only in the case of fibrocement did we assume a 2% renovation

rate according to local estimates. Third, maintenance involved cleaning tasks, e.g.,

removal and transport of sediments accumulated in the sewers. This data was available

in the case of Calafell and we considered the number of trips covered by the inspection

and maintenance service (48 trips/year; 75 km) and the average amount of sediments

(4,000 kg/year). We could not apply these estimates to Betanzos, but assumed a

negligible maintenance based on onsite observations.

All the construction flows were translated into monetary values through

MetaBase ITeC (2010) and CYPE Ingenieros (2015). The value assessment includes

additional costs, such as labor, overheads, fees and indirect costs (figure 1). Labor and

overhead data related to construction processes were available in the aforementioned

databases. O&M costs were retrieved from financial statements and invoices provided

by utility managers. In this case, the reposition costs of 2011 were obtained, but the

reposition rate was not available. Due to limited data availability, the economic costs

were not broken down into basic flows. The total cost of each sewer component is

provided in the Appendix S2.

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<Table 2>

<Heading level 2> Life cycle impact assessment (LCIA) and indicator selection

The selection of environmental indicators might be more complex when

communicating eco-efficiency results. In the eco-efficiency portfolios only one

indicator can be represented and selecting one or another might lead to the common

tradeoffs that occur in LCA studies. For this reason, we conducted the impact

assessment at three levels, i.e., using midpoints, endpoints, and a single score indicator.

These were modeled with the ReCiPe (H) method (Goedkoop et al. 2009) and the

Simapro 8 software (PRé Consultants 2014).

We used endpoints to determine the specific damage of the production,

installation, and O&M to human health, ecosystems and resources. As we were

interested in determining hotspots in the eco-efficiency of sewers, endpoints might

reduce the complexity of interpretations because decision-makers do not need to

identify the environmental relevance of each midpoint indicator (Bare et al. 2000). This

can also be achieved through an integrated single score indicator, which represents the

weighted endpoints in terms of eco-points (Pt). Although endpoint and single score

indicators have an increased uncertainty and subjectivity with respect to midpoints, we

used them in the eco-efficiency assessment for an easier understanding and

communication. Some argue that endpoints provide a more structured factor weighting

when comparing (Udo de Haes et al. 2002), as they are closer to our concerns, such as

health issues, and can be easily valuated (Hertwich and Hammitt 2001). Nevertheless,

there is a loss of comprehensiveness and increased uncertainty in endpoint and damage

analysis due to the modeling principles, assumptions and value choice (Bare et al.

2000).

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For this reason, a recommendation is to provide both the midpoint and endpoint

results to increase the transparency of the analysis (Kägi et al. 2016). We used a set of

18 ReCiPe midpoints and the Cumulative Energy Demand (CED) (Hischier et al. 2010)

to break down the environmental impacts into sewer components and O&M flows. By

doing so, we identified the impacts generated by basic flows (e.g., materials, energy,

etc.) at early stages of the cause-effect chain, such as the potential resource depletion or

pollutant emissions.

<Heading level 2> Economic indicator selection

The economic costs were calculated differently in the construction and O&M

processes. The O&M costs were based on the financial statement of the water facilities,

which include the energy, fees and indirect operation costs. In the case of the pipe

production and installation, the direct unit costs (DUC) resulting from the LCI were

converted into equivalent annual costs (EAC). By doing so, we accounted for the annual

costs of the sewer construction considering a time horizon of 100 years, which is the

potential maximum lifespan of concrete pipes. Equations (1), (2), and (3) illustrate the

conversion of the DUC into EAC. To calculate the total unit cost (TUC), we considered

that the indirect costs (IUC) were 10% of the DUC. The general costs (GUC) and

industrial profit (IP) represented 13% and 6% of the execution material budget (i.e.,

direct plus indirect costs), respectively (BOE 2001). A 3% interest rate was assumed to

estimate the present value (PV) and EAC, with a time horizon of 100 years according to

the FU of the analysis.

𝑇𝑈𝐶 = 𝐷𝑈𝐶 + 𝐼𝑈𝐶 + 𝐺𝑈𝐶 + 𝐼𝑃 = 1.309 𝐷𝑈𝐶 (1)

𝑃𝑉 = 𝑇𝑈𝐶

(1 + 𝑖)𝑡 (2)

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𝐸𝐴𝐶 = 𝑃𝑉×𝑖

1 − (1 + 𝑖)−𝑛 (3)

where TUC = total unit cost; DUC = direct unit cost; IUC = indirect unit cost; GUC =

general unit cost; IP = industrial profit; PV = present value; EAC = equivalent annual

costs; i = interest rate (3%); t = lifespan (present, t = 0); n = time horizon (100 years)

<Heading level 1> Results and discussion

In this section, we identified the life cycle stages with a poor environmental and

economic performance and sought possible explanations. These dimensions were

compared and eco-efficiency results were discussed in the context of the urban water

cycle.

<Heading level 2> Environmental and economic characterization of the sewers

A set of environmental and economic results is shown in table 3. The

environmental and economic hotspots were similar in both cities, but the total impacts

of Betanzos and Calafell were especially different. For instance, the impacts to human

health were 4.1E-07 and 6.9E-07 DALYs m-3, respectively, whereas the total economic

costs amounted to approximately one € m-3 in both cases.

<Heading level 3> Identification of environmental hotspots

The O&M was the most relevant phase of the environmental life cycle and

contributed to approximately 50% and 70% of the impacts to human health, ecosystems

and resources in Betanzos and Calafell, respectively. The main difference between both

cities was the energy required to pump wastewater. Within the O&M, the electricity

accounted for 30% and 70% of the impacts in Betanzos and Calafell, respectively.

These percent contributions to the endpoint indicators resulted from the midpoint

breakdown shown in figure 2 (the acronyms and absolute midpoint results are shown in

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Appendix S3). The ionizing radiation (IR) is the category where electricity contributed

most (around 90%), as 21% of the Spanish energy demand was covered by nuclear

power in 2011 (REE 2012). The contribution of the O&M to the life cycle impacts

might be even greater once the direct gas emissions are included in the assessment.

Besides the electricity consumption, the type of sewer component, material,

design and lifespan had a relevant effect on the results. The sewer components can be

classified in order from most to fewest impacts (figure 2). Depending on the impact

category, plastic pipelines accounted for the largest impacts, with a maximum

contribution of 40%, followed by appurtenances (30%) and concrete pipelines (10%).

The larger contribution of plastics can be easily associated with the length of sewer, as

these were the main materials used in the pipeline. As shown in Appendix S3, the pipe

itself had an irrelevant contribution to the total impacts (<10%), but the trench played a

key role in the construction stage as predicted by Petit-Boix et al. (2014, 2016). In this

case, we accounted for the worst case scenario, but Venkatesh et al. (2009) chose not to

include the trench materials because they were reused from the excavation. The impacts

of appurtenances were notable in the midpoints related to toxicity and metal depletion

because iron and steel parts were used in their construction (table 2). Based on these

results, the impacts of the O&M increased due to the reposition needs. Plastic pipelines

and appurtenances had shorter lifespans (50 years) than concrete pipes (100 years),

which means that the reposition was related to the components with the greatest

environmental impacts. An alternative might be to implement concrete pipelines that

have a longer service life and better environmental performance.

<Heading level 3> Identification of economic hotspots

Contrary to the environmental assessment, the installation stage resulted in the

largest economic investment (table 3). The cost of this stage amounted to 0.72-0.73 €

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m-3, which represented 70% and 75% of the total investment made in Calafell and

Betanzos, respectively. Because the O&M included the fees, personnel, and recurring

maintenance costs (named “others” in figure 2), we expected that these would account

for a greater share of the annual expenses. However, they represented 10% of the total

costs.

Labor was the reason why the installation was more expensive on an annual

basis. The need for skilled construction workers resulted in 50% of the investment at

this stage of the life cycle (see Appendix S2). In social terms, this investment might

result in positive effects, as it enhances the staff recruitment in the area. It was also

notable that plastic pipelines were the most expensive item in the system and accounted

for 60% of the construction costs in both cities, which was also associated with the

installation stage. As opposed to the LCA, note that we obtained real reposition costs

and did not apply the equivalent costs of the initial construction of the sewer. In this

case, the reposition was almost negligible.

<Table 3>

<Figure 2>

<Heading level 3> Explanatory variables to local differences

The environmental and economic trends were very similar in both case studies.

Nevertheless, the environmental effects of the O&M stage were greater in Calafell (e.g.,

5.1E-07 DALY m-3) than in Betanzos (e.g., 2.2E-07 DALY m-3). Previous analyses

tried to explain general variations in the O&M of sewers (Petit-Boix et al. 2015), but an

analysis of specific case studies might help to delve deeper into the differences among

cities.

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Different reasons might be associated with the energy requirements of these

sewers, which are 0.11 and 0.47 kWh m-3 in Betanzos and Calafell, respectively. Some

of them include the rainfall patterns, population, length of sewer, and location of the

WWTP. We checked each of these variables to determine which one might be

contributing most to the results of each city. Betanzos was expected to have an

increased energy demand because the Atlantic climate results in constant rainfall

throughout the year. Additionally, tides affect this region and might result in tidewater

entries to the combined sewer (Day 2000). However, these effects were not apparent

when comparing Betanzos to Calafell. The influence of population can be assessed

through the wastewater generation per capita. Based on table 1, we estimated a

wastewater production of 84 and 135 m3capita-1year-1 in Betanzos and Calafell,

respectively. Nevertheless, Calafell had a seasonal inflow of 13,227 tourists that

doubled the number of residents, so the total equivalent population should be applied

instead (table 1) (Idescat 2016). The resulting wastewater generation was 87 m3capita-

1year-1, which is similar to that of Betanzos and does not explain the difference in

energy consumption. The length of sewer needed to connect the city to the WWTP

might influence the electricity consumption as predicted by Petit-Boix et al. (2015).

Based on table 1, the length per m3 of wastewater was 0.05-0.07 km, which does not

explain the difference between the cities.

The last variable that we addressed was the location of the WWTP. Looking at

urban planning, Calafell’s WWTP was located at a higher altitude than that of Betanzos.

Although Betanzos had intermediate pumping stations to deal with topographic

variations, the WWTP was at sea level. Consequently, the annual energy intensity of the

pumping system was thirteen times greater in Calafell. A set of pumping stations

directed the wastewater flow to a larger station that was responsible for connecting the

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city to the WWTP through a rising sewer. The WWTP was three kilometers away from

this point and 40 m above sea level. For this reason, we believe that the main variable

that affected the O&M was the location of the WWTP.

<Heading level 2> Assessing the eco-efficiency of sewers

At this stage, we can apply the eco-efficiency portfolios to integrate the

environmental and economic results and facilitate the decision-making process. Because

the economic results (EAC) are based on an LCC, we showed the environmental effects

associated with economic investment, which is the eco-efficiency type called

environmental intensity of production (Huppes and Ishikawa 2005a).

In figure 3 we used a single score indicator to aggregate the environmental

impacts in a single unit. With this approach, we could identify the pathway towards eco-

efficiency in each life cycle stage. The shaded areas highlight the location of each life

cycle stage in the portfolio based on the case-study results. When compared to the other

life cycle stages, every euro invested in the O&M resulted in large environmental impacts.

Again, the highest values (e.g., 140 mPt/€) were associated with an increased energy

consumption in Calafell, which had a low economic cost (figure 2). The opposite

situation occurred in the installation stage. Here, the economic investment was high but

mainly related to labor costs, which do not have an environmental equivalent. However,

these might be an indirect measure of the number of workers involved, which could be a

positive social indicator. We found similar results when we used the global warming

instead of the single score indicator in the eco-efficiency representation (see the

Appendix S4).

The portfolio also provides some guidance on the pathway towards eco-efficiency

improvements. Given our findings on the effects of topography, a preliminary urban

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analysis is needed to find feasible locations of the WWTP that reduce the environmental

footprint of the system. In contrast, the main concern in terms of infrastructure was the

initial economic investment. When compared to the pipe and appurtenance production,

the installation might double the production impacts, but the costs had the largest room

for improvement, these being twelve times greater. In this case, the type of trench design,

which is concrete intensive, might require more labor hours than other solutions,

suggesting that an optimized system is needed.

It is also interesting to put the sewers into the context of the water cycle. As a

first estimation, we compared the eco-efficiency of our case studies with the average

eco-efficiency of Spanish WWTPs based on Lorenzo-Toja et al. (2016). Through this

comparison, we observed that the economic and environmental costs of Calafell’s sewer

were seven and two times greater than the WWTP average. When comparing it to

Betanzos, the environmental impacts did not differ, but the economic costs were also

seven times greater in the sewer. This is related to the construction phase, as the

environmental impacts of constructing WWTPs are negligible when compared to the

O&M (Lorenzo-Toja et al. 2016; Termes-Rifé et al. 2013) because of the lifetime of the

infrastructure. This showed that sewers are not irrelevant in the framework of the urban

water cycle, meaning that decisions made at the design phase will determine their

performance.

However, this can be challenging. The complexity of WWTPs is associated with

the efficiency of the O&M to meet water quality standards. In the case of sewers,

indirect decisions might result in greater effects than the mere selection of pipe

materials. Urban planning could have two main consequences on the eco-efficiency of

sewers. A distant WWTP results in a longer pipeline; if it is located at a higher altitude

than the city, this also involves more pumping energy. These decisions translate into

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avoidable economic investments in infrastructure and environmental burdens related to

pumping energy. Therefore, there is a need to envision sewers in the context of the

water cycle in order to design the system more eco-efficiently.

Still, sewer studies are underrepresented as compared to those dealing with the

impacts and costs of water and wastewater treatment. Loubet et al. (2014) found that the

environmental footprint of sewers is minimal in most studies, and the O&M contributed

to less than 10% of the total economic costs in a water cycle analysis elaborated by

Venkatesh and Brattebø (2011). Most of these analyses do not account for trench

materials or appurtenances and for this reason our results might be higher. In general,

more efforts are needed to characterize sewers under different conditions to better

understand their role in the water cycle.

<Figure 3>

<Heading level 2> On the application of eco-efficiency

Similarly to life cycle analyses, eco-efficiency is a robust communication tool,

but we believe that it has a greater outreach potential. The bi-dimensional nature of this

approach enables the benchmarking of product systems and it can be easily interpreted

by the general public. Some problems arise, though, when deciding the environmental

and economic indicators that define the product system. In our case, we used a measure

of the environmental intensity of production. This means that the optimum eco-

efficiency accounts for reduced environmental impacts generated through reduced

production costs. On the one hand, monetary costs and LCC are commonly used when

addressing the economic dimension, but one might argue that this approach is not

complete because it does not cover aspects such as economic growth or value creation

(Haes et al. 2004). On the other hand, we selected a set of indicators, but standards

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should provide some guidance and discuss the suitability of aggregated indicators in the

context of eco-efficiency communication tools.

We proved that the procedure presented in ISO 14045:2012 can be applied to

urban systems and provided integrated data for the decision-making process. An

optimized system might serve as a reference for sewer benchmarking, but we did not

provide this result because several parameters are at play. For instance, policies and

social perceptions should be accounted for, as these determine the location and

configuration of the sewer. Our approach serves as a first step towards integrating

economic and environmental variables in the context of urban sanitation, which is

helpful to decision-makers and might in fact change the social aspects associated with

the impacts of sewers. Urban systems are a good example of micro-scale effects to

macro-scale eco-efficiency, which is an approach to consider in order to avoid tradeoffs

(Huppes and Ishikawa 2005b). If service providers (e.g., pipe manufacturers) improve

their eco-efficiency, these might become more competitive in the market and result in

further positive effects in the context of the urban water cycle and the overall

performance of our cities.

<Heading level 1> Conclusions

The eco-efficiency approach helped us to determine key hotspots in the

environmental and economic performance of sewers. We studied two case studies with

contrasting features in terms of population, climate, urban and sewer configuration, and

yet we obtained similar trends. The critical life cycle stages were the O&M in

environmental terms, and the installation in economic terms. The impacts of the O&M

were associated with the location of the WWTP and the consequent energy needs. Labor

was the main economic flow that affected the investment in the installation of sewers.

This factor should be further assessed, as it might entail social benefits that are not

19

directly captured by the eco-efficiency approach. Additionally, one of the sewers

resulted in seven and two times as many economic and environmental impacts as an

average WWTP. This means that sewers are in a critical and challenging position that

calls for an integrated assessment of the urban water cycle.

To the authors’ knowledge, this is the first application of ISO 14045:2012 to

sewers. We believe that this is a method with a great potential in terms of

communication, although integrating further social aspects should be considered. This

study suggests that this type of assessment may well encourage water managers and

local administrations to implement more sustainable alternatives in facility planning and

management. Benchmarking their performance might be a compelling approach, as it

shows their improvements with respect to similar services and drives their pathway

towards a more eco-efficient behavior.

<Heading level 1> Acknowledgements

We performed this study thanks to the LIFE+ Aquaenvec project

(LIFE10/ENV/ES/520) “Assessment and improvement of the urban water cycle eco-

efficiency using LCA and LCC”. The authors are grateful for the support of the Spanish

Ministry of Education for the grant awarded to A. Petit-Boix (FPU13/01273) and

Generalitat de Catalunya for funding the 2014 SGR 1412. The authors acknowledge the

financial support from the Spanish Ministry of Economy and Competitiveness, through

the “María de Maeztu” program for Units of Excellence in R&D (MDM-2015-0552).

The authors have no conflict of interest to declare.

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About the authors

28

Anna Petit-Boix is currently a PhD student at the Sostenipra research group from the

Institute of Environmental Science and Technology (ICTA), in the Autonomous

University of Barcelona (UAB) in Bellaterra (Catalonia, Spain).

Carla Arnal is an economist researcher at Cetaqua, Water Technology Center in Cornellà

de Llobregat (Catalonia, Spain)

Desirée Marín is Head of the Environment, Society & Economics research program at

Cetaqua, Water Technology Center in Cornellà de Llobregat (Catalonia, Spain)

Alejandro Josa is a senior researcher and professor at the Department of Civil and

Environmental Engineering, the School of Civil Engineering and the Institute of

Sustainability (IS.UPC) of the Technical University of Catalonia (UPC) in Barcelona

(Catalonia, Spain)

Xavier Gabarrell is a senior researcher and professor at the Department of Chemical,

Biological and Environmental Engineering (UAB) and the Sostenipra research group in

Bellaterra (Catalonia, Spain).

Joan Rieradevall is a senior researcher and professor at the Department of Chemical,

Biological and Environmental Engineering (UAB) the Sostenipra research group in

Bellaterra (Catalonia, Spain).

29

Figure 1 System boundaries of the LCA and LCC of sewers

30

Figure 2 Distribution of the environmental and economic impacts of the sewer

components and O&M flows of the sewers in Calafell and Betanzos

0%

20%

40%

60%

80%

100%

Concrete pipeline Plastic pipeline Appurtenances Pumping energy

Cleaning Reposition Others

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Betan

zos

Calafell

Rel

ativ

e co

ntr

ibuti

on

EA

C

GW

OD

TA

FE

ME

HT

PO

F

PM

F

TE

T

FE

T

ME

T

IR

AL

O

UL

O

NL

T

WD

FD

MD

CE

D

31

Figure 3 Eco-efficiency portfolio illustrating the differences amongst life cycle stages in

Betanzos and Calafell

32

Table 1 Main features of the sewer networks in the cities analyzed. Based on

data provided by the local water managers for the year 2011.

A) General features

Betanzos Calafell

Climate Atlantic Mediterranean

Year-round population 13,537 24,984

Total equivalent population (year-round + tourism) 13,672 38,211

Wastewater production (m3/year) 1,145,699 3,349,749

Pumping energy (kWh/year) 121,591 1,577,054

B) Pipeline composition

Betanzos Calafell

Material Diameter (mm) Length (m)

Concrete

250 721 929

300 22,081 22,718

350 0 7,704

400 0 3,697

500 120 7,053

600 381 896

700 0 1,065

800 0 1,883

1000 0 553

1200 819 251

Fibrocement 400 1,518 0

HDPE

110 727 0

200 243 11,856

250 0 4,438

300 0 67,660

350 0 2,208

400 0 21,540

450 0 2,489

500 0 9,369

700 0 1,680

800 0 4,766

1200 0 700

PVC

75 819 0

90 943 0

110 57 0

200 3,431 0

250 8,654 0

315 35,249 0

400 1,700 0

Total pipeline 77,462 173,454

33

C) Appurtenance composition (in number of units)

Betanzos Calafell

Manhole 1,578 4,154

Inspection chamber (30x30 cm) 21 201

Inspection chamber (50x50 cm) 1,556 3,458

Inspection chamber (100x100 cm) 22 495

Submersible pump (60 m3/h) 13 15

Scupper 1,599 1,199

Wastewater connection 2,638 9,239

34

Table 2 Life cycle inventory divided into the construction and O&M in the case study

cities. Data per FU (1 m3 of wastewater)

n.d. = no data

Flows Betanzos Calafell

Quantity Units Quantity Units

Production and installation

Mass concrete pipe 2.2E-02 kg 1.8E-02 kg

Fibrocement pipe 9.6E-04 kg 0 kg

PVC for pipe and appurtenance 1.4E-03 kg 9.9E-05 kg

HDPE for pipe 2.0E-05 kg 6.3E-03 kg

Synthetic rubber 2.9E-06 kg 7.6E-05 kg

Polyurethane 1.3E-05 kg 0 kg

Extrusion process 1.4E-03 kg 6.4E-03 kg

Cement mortar 5.8E-03 kg 4.6E-03 kg

Concrete 8.2E-05 m3 6.1E-05 m3

Concrete block 5.6E-02 kg 5.2E-02 kg

Sand 4.2E-01 kg 4.1E-01 kg

Gravel 1.5E+00 kg 1.3E+00 kg

Wood 1.7E-05 m3 1.3E-05 m3

Cast iron 3.3E-03 kg 2.7E-03 kg

Stainless Steel 4.1E-06 kg 1.3E-06 kg

Metal product manufacturing 3.4E-03 kg 2.7E-03 kg

Diesel 1.6E-01 MJ 1.4E-01 MJ

Transport 1.3E-01 tkm 1.2E-01 tkm

Operation and Maintenance (O&M)

Electricity 1.1E-01 kWh 4.7E-01 kWh

Mass concrete pipe 0 kg 0 kg

Fibrocement pipe 1.9E-05 kg 0 kg

PVC for pipe 1.4E-03 kg 9.9E-05 kg

HDPE for pipe 2.0E-05 kg 6.3E-03 kg

Synthetic rubber 2.9E-06 kg 7.6E-05 kg

Polyurethane 1.3E-05 kg 0 kg

Extrusion process 1.4E-03 kg 6.4E-03 kg

Cement mortar 4.7E-03 kg 3.9E-03 kg

Concrete 1.4E-05 m3 1.1E-05 m3

Concrete block 5.6E-02 kg 5.2E-02 kg

Sand 3.4E-01 kg 3.5E-01 kg

Gravel 1.2E+00 kg 1.2E+00 kg

Wood 1.3E-05 m3 1.1E-05 m3

Cast iron 3.5E-03 kg 2.7E-03 kg

Stainless Steel 1.9E-05 kg 7.2E-06 kg

Metal product manufacturing 3.5E-03 kg 2.7E-03 kg

Diesel 1.2E-01 MJ 1.1E-01 MJ

Transport 1.0E-01 tkm 9.7E-02 tkm

Sand removal and transport n.d. tkm 4.5E-03 tkm

35

Table 3 Environmental and economic results of Calafell and Betanzos divided into life

cycle stages (Data per FU: 1 m3)

City Dimension Indicators Units Producti

on Installation O&M Total

Betanzos Environment Human Health DALY 6.1E-08 1.3E-07 2.2E-07 4.1E-07

% contribution 15% 32% 53% 100%

Ecosystems species.yr 2.3E-10 1.1E-09 1.3E-09 2.6E-09

% contribution 9% 42% 49% 100%

Resources $ 1.7E-03 3.0E-03 5.7E-03 1.0E-02

% contribution 16% 29% 55% 100%

Economy AEC € 0.06 0.73 0.19 0.98

% contribution 6% 75% 19% 100%

Calafell Environment Human Health DALY 7.0E-08 1.1E-07 5.1E-07 6.9E-07

% contribution 10% 16% 74% 100%

Ecosystems species.yr 2.8E-10 9.0E-10 2.4E-09 3.6E-09

% contribution 8% 25% 67% 100%

Resources $ 2.9E-03 2.6E-03 1.4E-02 1.9E-02

% contribution 15% 14% 71% 100%

Economy AEC € 0.10 0.72 0.21 1.03

% contribution 9% 70% 20% 100%